The present invention is directed to automated analyzers and, more specifically, is directed to a temperature regulator assembly for a stream processing reactor in an analyzing instrument. Color development in the detection system of an amino acid analyzer has been selected as a represented application.
In some amino acid analyzers, a very small or micro chromagraphic column is used as a specialized application of a liquid column chromatographic separation technique, utilizing ion exchange resin as the stationary phase and eluting buffers of varying pH and salt concentration as the moving phase. Amino acids contained in a sample are introduced at the top of the column and are separated from each other as they are eluted through the resin bed which comprises the column packing. For amino acid analysis, the method for detecting the amino acids in the effluent stream has been to combine the column effluent with a reagent that is metered into the stream at a flow rate proportional to that of the column eluent. When the reagent combines with the amino acids present in the stream, compounds are formed which, when subjected to further development process can be detected by specific changes in optical properties such as absorption or fluorescence.
One of the classical detection methods in amino acid analyzer systems is that developed by Spackman and Moore, wherein the reagent used is ninhydrin dissolved in a suitable solvent/buffer solution. Under this process, the column effluent/reagent solution is heated in a reactor to a fixed temperature for a specified period of time. The compound developed as a result of this process will have specific colors, the intensities of which are proportional to the amounts of compounds contained in the flowing stream. The optical density of these compounds is measured at specific wavelengths.
Important to the calibration of the analyzer in terms of its specific sensitivity to detect amino acids is that the fluid/reagent mixture be maintained at a constant elevated temperature for a fixed period of time. It is critical to the stability of the instrument calibration that the two parameters of temperature and exposure time remain constant during the color development process. Classically, this had been accomplished by causing the effluent to pass through a TFE capillary coil which is normally suspended in a boiling water bath to act as the reactor in the amino acid analyzer system.
The separation techniques employed in early analyzers required several hours to complete a single analysis. In such systems, it became common practice to retain the flowing stream within the reactor for as long as fifteen minutes to complete color development. Newer techniques have increased the performance of these analyzers to permit the same analyses to be completed in the order of twenty minutes. It then becomes necessary to provide increased color development in a much shorter period of time. Reference is made to FIG. 1 showing empirical results of studies which relate the optical densities of compounds formed by mixtures of amino acids and ninhydrin as function of development time and temperature.
It may be noted that maximum sensitivity and improved resolution can be obtained by operating the color development reactor at temperatures significantly above 100.degree. C. However, operation at these elevated temperatures introduces several critical problems. It is very important that circumstances must be prevented which would cause or induce the boiling of the liquid passing through the reactor. Further, high temperature in conjunction with the fact that the pH of the solutions alternate between base and acids increases the corrosive nature of the liquids. Also, it is important that the reactor not be damaged by the heat and, therefore, the system must provide rapid cooling of the reactor in the event there is some type of catastrophic loss of fluid flow caused by a loss of control in the system.
Prior approaches utilizing some type of heated bath as the temperature control for a coil shaped reactor are shown in U.S. Pat. No. 3,806,321 (Durrum); No. 4,233,030 (Twitchett); No. 3,926,800 (Stephens); and No. 3,918,907 (Stephens). Attention is also directed to co-pending patent application entitled An Analytical Instrument Temperature Regulator Ser. No. 327,372, filed Dec. 4, 1981, in the names of Donald E. Stephens and Robert J. Ehret and assigned to the assignee of the present invention.
However, these prior systems do not provide the ability to heat to the desirable temperatures above 100.degree. C. with the capability of rapid cool down to prevent boiling of the fluid stream and prevent possible damage to the materials from which the reactor is made.